To begin with check their reaction, just put them down next to the kittens and let them out of their carriers, either they'll not care and be perfectly fine or they'll hiss and hit the kittens, personally I always carefully watch but let the cats assert their dominance instead of trying to stop it, it takes them less than 2 days to get over it and just curl up with them, the hissing doesn't hurt the kittens and unless you see their claws out when they're slapping the kittens it doesn't hurt them either, you could always keep them in a separate room and give supervised visits while you're there though that may take longer, if the older ones are neutered they're likely to not be as bothered by the kittens as they don't see them as a threat, just don't punish or make it seem like hissing is a bad thing or they'll get jealous and start seeing them as a threat, also make sure that their food and litter is separate from the kittens for a little while so they don't feel the need to protect their things